# How do I know whether the major axis of an ellipse is horizontal or vertical?

Sep 28, 2014

Locate the larger of the 2 denominators. Then look at that numerator.

If it has an $x$ then that is the major axis. Horizontal
If it has an $y$ then that is the major axis. Vertical

${x}^{2} / 4 + {y}^{2} / 16 = 1$

The major axis is $y$. Vertical

${x}^{2} / 25 + {y}^{2} / 16 = 1$

The major axis is $x$. Horizontal